A sudden death associated with the use of sodium nitroprusside for induction of hypotension during anaesthesia.

A death from cyanide poisoning during operation was attributable to the use of approximately 400 mg (10 mg per Kg) sodium nitroprusside as an hypotensive agent. Autopsy cyanide levels of 0.5 mg per cent in blood and 0.3 mg per cent in urine and thiocyanate levels too low to measure in either, suggest an abnormality of cyanide metabolism. The lethal dose of sodium nitroprusside appears to be 7 mg per Kg. A safe regimen would be 3.5 mg per Kg as the anticipated total dose for the period of hypotension. Patients resistant to the full hypotensive effects of sodium nitroprusside, or unable to maintain the level of hypotension, or requiring more than 3.5 mg per Kg to achieve the required effect for the anticipated time, may accumulate toxic levels of cyanide in the blood. Patients with Leber's optic atrophy, tobacco amblyopia and possibly those with other nerve atrophies should not receive sodium nitroprusside or any other cyanide precursor.